The present invention relates generally to liquid agitators, and more particularly relates to agitators for use in developing photographic film.
When developing photographic film it is necessary to keep the developing solution properly mixed in order to obtain sharp, properly shaded pictures. If the developing solution is mixed or agitated too little, the film becomes cloudy. If the developing solution is agitated too much the developing process takes place too rapidly and the film becomes dark such that midtones or shading is lost. This need for proper agitation of the developing solution requires, in the absence of some automatic apparatus for agitating the solution, almost constant supervision during the developing process.
Numerous attempts have been made to provide devices for agitating developing solution which did not require constant supervision, but for various reasons these have met with only limited success. One such prior art device is shown in U.S. Pat. No. 2,104,283 which issued to Robert A. Webster on Jan. 4, 1938. This patent discloses a reversible motor driving an upright shaft which carries a tray at its upper end to support a developing tank. According to this patent, the oscillating motion of the shaft keeps the solution well mixed and the sudden reversing motion at the end of each power stroke of the reversible motor causes a washing action on the film to remove any gas bubbles which may have adhered to the film. The principle disadvantage with this device is that it is constantly agitating the developing solution and this can easily result in over-agitation.
Another prior art agitator is disclosed in U.S. Pat. No. 2,545,914 which issued to H. F. Boucher on Mar. 20, 1951. This patent discloses a device which constantly oscillates a film reel within a developing tank. However, if the film reel is oscillated fast enough to insure that gas bubbles adhering to the film are removed, the constant oscillation will result in over-agitation.
Still another prior art agitator is disclosed in U.S. Pat. No. 2,493,441 which issued to W. H. Carr, Jr., on Jan. 3, 1950. This patent discloses an agitator which imparts an intermittent rocking motion to a developing tank. That is, the developing tank is oscillated about a horizontal axis rather than an upright axis. However, experience has shown the gentle agitation resulting from oscillation about an upright axis provides better results than the relatively violent agitation caused by oscillation about a horizontal axis.